Process for protecting metal from corrosion



Nov.-7, 1961 L.V.COLL1NGS 3,

PROCESS FOR PROTECTING METAL FROM CORROSION Filed Feb. 6, 1958 3 Sheets-Sheet 1 FIG.|

WEIGHT LOSS "000 OFFER u PUMPED om 1.MCCLMNRL....L..........L...;l

LEGEND TP coupons MIDDLE 8 LOW TYPE OF BALLAST COUPONS AVERAGEIJI W MEN...

Lawrence V. Collings FRESH SEA BRACKISH r ATTORNEYS Nov. 7, 1961 L. v. COLLINGS 3,007,811

PROCESS FOR PROTECTING METAL FROM CORROSION Filed Feb. 5, 1958 FIG 2 r"COFFERD 3 Sheets-Sheet 2 A WATER BALLAST TIME.

OFFERDAM R BASED ON RETREATMENT L'JUNE JULY AUG! SEPT. LOCT.

INVENTOR 7 Lawrence V. Collings ATTORNEYS Nov. 7, 1961 L. v. COLLINGS 3,007,8

PROCESS FOR PROTECTING METAL FROM CORROSION Filed Feb. 6, 1958 3 Sheets-Sheet 3 COFFERDAN UNDER SEA WATER BALLAST APPROX. 50% OF THE TIME.

FIG.3

WEIGHT L SS GRAMS LOCT. L- wovw-L DECL-J INVENTOR. LawrenceV. Col lings (lir W ATTORN EY S 3,007,811 Patented Nov. 7, 1961 Bee Filed Feb. 6, 1958, Ser. No. 713,586 2 Claims. (Cl. 117--97) This invention relates to a method for protecting metal surfaces against corrosion. More particularly, it relates to the application of an adherent protective coating of a composition comprising mineral lubricating oil, barium mahogany sulfonates, zinc dithiophosphate and an alkyl phenyl phosphate to the interior surfaces of cargo tanks, ballast tanks, cofferdams, bilges, voids and rudders of ocean-going tank ships and ore carriers, as Well as to the surfaces of dry docks, fire tower water tanks and the like.

Oil-type marine tank coating compounds have found wide usage in the coiferdams of tank ships and in ore and other dry cargo carriers where cargo contamination is not a problem. These inhibitors can be applied by brush or sparying. However, the preferred method of application, since it economically affords a continuous and uniform protective coating on the interior surfaces of the tank, is to float a suincient quantity of a suitable fluent corrosion inhibitor on the surface of ballast water as the tank is being filled therewith or emptied thereof and to effect the coating of the tanks interior walls by the movement of the Waters surface relative to such walls. What is a sufficient quantity of the corrosion inhibitor is, of course, determined by what thickness the protective layer should have over the surface it coats and the thickness, in turn, depends on the nature of the coating material and the service requirements it must undergo. Thus, for instance, in the case of ocean-going ships, service requirements for coating materials are unusually severe, since they must have the ability to penetrate heavy rust deposits and to displace salt Water in contact with tank surfaces. Further, the rust inhibiting material must be effective not only in empty tanks subject to high humidity and salt air, but also in tanks that are completely filled with sea water.

I have now discovered a novel process for protecting the interior surfaces of cofferdams, i.e., 3 to 4 feet wide spaces between bulkheads extending the Width of a ship and separating cargo tanks or bins from the engine room and ships fuel tanks, and similar enclosures from the corrosive efiects of sal air and salt water. This process entails introducing into such metallic enclosure a fluent coating composition comprising the following mixture: 90.0 to 98.5 Weight percent of a mineral oil, preferably one having lubricating oil viscosity characteristics; 0.5 to 5.0 weight percent barium mahogany sulfonate; 0.5 to 1.8 weight percent zinc dithiophosphate; and, 0.3 to 3.5 weight percent alkyl phenyl phosphate. I have found it advantageous to include an anti-foam agent in this composition, such as a silicon polymer having a viscosity of 100 centistokes at 25 C. and known commercially as DCF (Dow Corning Fluid No. 200-100). The antifoam agent, when employed, is present in amounts of about 0.0005 to 0.0015 weight percent. The corrosion inhibiting compound preferably used in my process has the following composition: about 96.7 weight percent of mineral lubricating oil; about 2.0 weight percent of bariurn mahogany sulfonate; 0.7 weight percentof zinc dithiophosphate; about 0.6 weight percent alkyl phenyl phosphate; and, if desired, about 0.001 weight percent of the DCF.

After the introduction into the space to be protected of such a composition, my process further entails the floating of the composition upon the surface of a body of Water admitted into the enclosure and coating its walls and structural members with the composition by means of the relative movement between the surface of the body of water and the internal surfaces of the enclosure. Thus, the coating can take place either as a result of raising and lowering the surface of the body of water within the enclosure while the enclosure itself remains stationary or as a result of the tendency of the surface of the body of water to remain in a horizontal plane even when the enclosure is inclined in any direction from its usual position. Of the two, of course, the first is preferred, since it more readily alfords retreatment of the entire internal surface area sought to be protected.

For the best results, the process of my invention should be undertaken when the enclosure, e.g., a colferdarn, is empty and when enough of the corrosion inhibitor oil is available to afford an appreciable oil film thickness on the ballast surface. This thickness should be at least a thirty-second of an inch ($5 One 55 gallon drum of the corrosion inhibitor of my process will cover a stuface area of four feet by eighty feed (4' x with a layer one quarter of an inch (MW) thick. Further, since corrosion is most severe on the underdeck, the uppermost areas of the tank should be coated during every ballasting period, preferably at intervals not exceeding six months. Again, the process should be carried out by slowly raising the corrosion inhibitor oil film into the expansion trunk coamings by pumping sea water or, preferably, fresh water into the bottom of the tank. The process of the invention produces very effective results with sea water ballast if it is properly managed, but use of the less corrosive fresh water results in very low corrosion rates. By proper management is meant that the ballast water should be added at a rate which will raise the ballast surface no faster than about five feet an hour.

For an initial treatment, the amount of corrosion inhibitor oil employed in my process will depend on the amount of rust cake within the coiferdam. For new, or lightly rusted steel surfaces, for instance, onefourth of a gallon of the oil per ton of cofferdam Water capacity is adequate to provide a coating of suitable thickness on the metal surfaces. For heavily rusted surfaces, at least one gallon of the oil per ton is preferred. And it should be noted, in passing, that a thin film of rust is often beneficial in that it retains the rust preventive oils on the steel surface by blotter or wick type action. However, the precise efliciency of the rust preventive oil will be determined to a great extent by whether the rust film is wet with water when the oil is applied. The oil penetrates a dry rust film more rapidly and more effectively. Hence best results will be obtained by employing my process in a dry coiferdam such as is available immediately after the shipyard has been left or after a period of ventilating with dry air.

Each of the compounds making up the composition employed in my process is commercially available. For example, the mineral lubricating oil can be a solvent refined or distilled neutral oil, solvent refined bright stock or the like or blends of two or more lubricating oil fractions and can be derived from Mid-Continent, napthenic or Pennsylvania crudes. An advantageous blend consists of about 52 volume percent of a solvent-refined Mid-Continent neutral oil having a viscosity of about 200 SUS at .F. and about 48 volume percent of a solventrefined Mid-Continent bright stock having a viscosity of about SUS at 210 F. This blend has a viscosity of about 66 SUS at 210 F.

The barium mahogany sulfonates in the composition employed in my process are those obtained by neutralizing the oil-soluble petroleum sulfonic acids obtained in conventional treatment of lubricating oil fractions with oleum to produce medicinal and other highly refined oils. More particularly, a lube oil fraction is contacted with oleum, sulfur trioxide or other sulfonating agents, the resulting sludge layer is separated and the mahogany sulfonic acids contained in the oil layer are neutralized with barium oxide in water. These sulfonates can be produced by various methods to provide noimal or basic sulfonates. When the sulfonate is basic, I prefer that at least about 1.5 times the amount of barium be present than is needed to provide a neutral or normal sulfonate. A carbonated sulfonate which can be employed can be obtained by contacting the mahogany sulfonate, e.g., a basic barium sulfonate, with carbon dioxide until the strong basicity of the sulfonate to phenolphthalein is reduced and a final pH of about 7 to 8.5 is obtained. This can be carried out, for example, by introducing the sulfonate to the top of a packed column and then feeding carbon dioxide to the bottom of the tower. The carbonated mahogany sulfonate is then recovered and vacuum dried to obtain the final product. As an example, a typical carbonated basic barium sulfonate prepared from an oleum treated West Texas gas oil fraction analyzed 2.86 percent barium and had a Base No. to pH 4 of 11.3. The sulfonate usually contains unreacted lubricating oil which can be added to my corrosion inhibiting process compounds as part of the base oil.

The zinc dithiophosphate oxidation inhibitor and the alkyl phenyl phosphate components of the corrosion inhibiting compounds used in my process are well known. In general, the zinc dithiophosphates to be employed contain about 3 to 18 carbon atoms in the organic radical and preferably 3 to 10 carbon atoms. Zinc dithiophosphates can be made by any known procedure, e.g., by contacting the reaction product of a suitable alcohol and phosphorus pentasulfide with Zinc oxide. The alkyl phenyl phosphates employed contain one or two alkyl groups per molecule with each alkyl chain having about 3 to 18 carbon atoms and, preferably, 3 to 10 carbon atoms; in the dialkyl forms, the alkyl radicals need not be the same. Mixtures containing monoalkyl and dialkyl phenyl phosphates can also be employed. Alkyl phenyl phosphate, dialkyl phenyl phosphates are prepared typically by reacting phosphorus pentoxide with a commercial grade phenol, e.g., diamyl phenol, at an elevated temperature on the order of 275 F. Typical examples of satisfactory phosphates include monoand dibutyl phenyl phosphate, dipropyl phenyl phosphate, hexyl phenyl phosphate, dihexyl phenyl phosphate, pentyl hexyl phenyl phosphate, etc. The alkyl phenyl phosphate and metal dithiophosphate can also be obtained in solution in lubrieating oil which can be added as part of the base oil of my corrosion inhibiting process compounds.

Compositions used in the present invention can be made without observing special conditions of temperature, pressure, order of mixing or the like. For example, each of the components may be added to the oil base separately, or the zinc dithiophosphate, alkyl phenyl phosphate, and barium mahogany sulfonate can be pre-mixed in the desired proportions and then added to the oil base. As a practical matter, it is preferred to heat the resulting mixture to about 100 F. to facilitate rapid solution and to stir the mass to insure a homogeneous mixture.

For a further understanding of the invention, reference should be had to the following example.

EXAMPLE I A composition (X in the tables, infra) was made by adding 1.5 pounds of a zinc dithiophosphate-oil mixture (47 weight percent dithiophosphate-SB weight percent oil) in which the zinc dithiophosphate was obtained by reacting zinc oxide with the reaction products of P 8 and methyl amyl alcohol; 1.0 pound of a diamylphenyl phosphate-oil mixture (60 weight percent phosphate-40 weight percent oil); 7.8 pounds of a carbonated barium mahogany sulfonate-oil mixture (25 weight percent sulfonate75 weight percent oil); 89.7 pounds of a mineral oil blend composed of 52 volume percent of a solventrefined Mid-Continent neutral oil having a viscosity of about 200 SUS at F. and about 48 volume percent of a solvent-refined Mid-Continent bright stock having a viscosity of 120 SUS at 210 F.; and, 0.001 pound of DCF 200-100. This composition had the following characteristics:

Samples of this composition were subjected to three types of rust test and compared therein against several commercial available marine coating compounds (A to E). With regard to flash points and viscosity, these compounds compare as follows:

Compound Flash Pt Vis./100 F.

F (SUS) Min. 435 5204500 Compounds A to B were similar in appearance. All were black and, apparently, used residual fuel or similar material as base oil. Simple laboratory tests to determine wetting ability indicated that compounds A to E contained supplemental wetting agents for better displacement of water from metal surfaces. No attempt was made to identify any rust inhibitors present. However, tests indicated that the compounds function primarily by setting up a barrier film of asphaltie material on the surface of the metal. Both C and D air-dried to a hard asphalt-like coating and probably are intended for use where air drying is possible. However, because of the high viscosity of C, this compound is unsuitable for application by flotation and brushing or spraying is required.

The three types of tests to which A to E and X were subjected included (1) humidity cabinet exposure to simulate conditions in empty tanks aboard ship; (2) immersion tests to simulate conditions in ballasted tanks aboard ship; and, (3) dynamic tests to simulate conditions in the splash zone of tanks aboard ship. The results of these tests are tabulated in Table I.

TABLE I (1 21260 humidity cabinet (100% relative humidity- Sand blasted coupons dipped in boiling 5% NaCl solution and dried to give salt contaminated surface. Coupons were coated with compounds listed and exposed in humidity cabinet 24 hours.

(2) Static test Compound: Wt. loss, gm.

Blank (no inhibitor) 0.3341 Residual fuel 0.2439

A B C D- E X (3) Dynamic test Measured quantity of compounds floated on surface of 800 ml. 2% NaCl solution in square quart bottle. Sand blasted coupon immersed through floating compounds into solution. Bottles rotated at 17 rpm. in turntable apparatus for'3 or 10 days at room temperature. The tests Were run in triplicate.

l Corresponds to 1 drum (55 gal.) oi compoimd per 100 tons sea Water capacity.

EXAMPLE II Further samples of the composition of Example I were tested in trials using pro-rusted steel. Sand blasted coupons were pre-rusted to give heavy continuous coatings of salt contaminated rust scale for use in a humidity cabinet test and a static test as those tests are defined in Example I. The results of these tests are given in Table II.

(1) 21260 humidity cabinet test (95% relative humidity] F.)

Pre-rusted coupons run blank or dipped in X. Test duration 5 days.

Blank:

Wt. loss, gm., resulting from pro-rust Total Wt. loss, gm., resulting from pre-rust plus 5 days in humidity cabinet Ditferences wt. loss, gm., resulting from 5 days in humidity cabinet 1.7688 (8 tests run).

3.4383 (7 tests run).

Dipped in X Wt. loss, gm., resulting from pre-rust Total wt. loss, gm., resulting from pre-rust plus 5 days in humidity cabinet Differencezwt. loss, gm., resulting from 5 days in humidity cabinet Percent protection from X 1.9607 (7 tests run).

(2 Static test Pro-rusted coupons approximately 50% immersed in 2% NaCl solution. Beakers were placed in humidity cabinet (95% relative humidity-100 F.) for 10 days.

Blank:

Wt. loss, gm., resulting from pre-rust Total wt. loss, gm., resulting from pre-rust plus 10 days in humidity cabinet Diifereneezwt. loss, gm., resulting from 10 days in humidity cabinet 1.7688 (8 tests run).

2.7363 (7 tests run).

Dipped in X Wt. loss, gun, resulting from pre-rust Total wt. loss, gm., resulting from pre-rust plus 10 days in humidity cabinet Difierencezwt. loss, gm, resulting from 10 days in humidity cabinet Percent protection from X 1.7688 (8 tests run).

1.9443 (7 tests run).

EXAMPLE I'II On December sixteenth, four drums of composition of Example I were applied by flotation on fresh, potable water to the after coiferdam of an ocean-going tanker. The concentration of the composition used was, roughly, one drum per fifty tons cofferdam capacity. Varying corrosion rates produced by varying conditions within the tank were then determined by the evaluation of weight loss coupons installed high, midway down and low in the tank. Both the weight lost, in grams, and the corrosion rates, in mils per year, are shown on the graph at tached hereto which is embodied in FIGURES 1 to 3.

For a clearer understanding of FIGURES 1 to 3, reference should be had to Table III. Column 1 of Table III shows the period of time during which the coupons installed on December sixteenth were exposed to various ballasts in the cofferdam. Column 2 shows the dates on which readings were taken. Column 3 shows the average Weight lost by the top coupons in grams. and the calculated corrosion rate as of such dates in mils per year. Column 4 shows the average weight lost by the middle and bottom coupons in grams and the calculated corrosion rate as of the reading dates in mils per year. The data in column 3 has been plotted as an unbroken line in the graph of FIGURES 1 to 3. The data in column 4 has been plotted as a broken line in the graph of FIGURES 1 to 3.

Further, it will be noted that dotted coordinates employing the weight loss figures of 15 :1442 gm. for the top coupons and 3.980 1 gm. for the middle and low coupons, i.e., the weight loss figures obtaining on July fifth after six and one half months exposure and before the treatment of the coiferdam on that date with two drums of composition X of Example I, as base lines have been included in FIGURES 2 and 3. This has been done to show that both the weight loss figures and the corrosion rates for the period after July fifth were substantially decreased by the retreatment.

The shaded areas in FIGURES l and 2 indicate the types of ballast, i.e., fresh water, sea water and brackish Water, employed and, in addition, the time spans in days during which they were employed. It is, however, to be understood that in the period after July fifth, shown in FIGURES 2 and 3, the coiferdam was under sea Water ballast and for about 50 percent of the time.

FIGURES l and 2 show fresh water ballasting at intervals during the period from December to about March twenty-first produced slight corrosion. Low corrosion rates were obtained in spite of the fact that nearly all of the floating corrosion inhibiting compound was pumped out on about January seventeenth and no more was placed in the cofierdam until July fifth. On the other hand, sea Water, introduced into the cotferdam without a floating film of corrosion inhibiting compound between March and July, caused substantial corrosion. However, upon introduction of a fresh film of the corrosion inhibiting compound into the coiferdarn on July fifth, the amounts and rates of corrosion in the period thereafter were appreciably lowered. This is particularly reflected in FIGURES 2 and 3.

RETREATMENI ON 7/5 WITH TWO DRUMS OF COMPOSI- TION X OF EXAMPLE I I claim:

1. A method for protecting the internal surface of a metal tank from the corrosive effects of salt laden air and salt Water corrosion consisting essentially of introducing into said tank a fluent coating composition comprising an intimate mixture of from 90.0 to 98.5 Weight percent of a mineral lubricating oil, from 0.5 to 5.0 weight percent barium mahogany sulfonate, from 0.5 to 1.8 Weight percent zinc dithiophosphate and from 0.3 to 3.5 weight percent alkyl phenyl phosphate, floating said coating composition upon the surface of a body of water in said tank and coating said internal surfaces with said coating composition by effecting relative movement between the surface of said body of water and said Walls.

2. The method of claim 1 in which the intimate mixture consists essentially of about 96.7 weight percent of a mineral lubricating oil, said mineral lubricating oil having a viscosity of about 66 SUS at 210 F. md. including about 52 volume percent of a solvent-refined Mid-Continent neutral oil having a viscosity of about 200 SUS at F. and 48 volume percent of a solvent-refined Mid- Continent bright stock having a viscosity of about SUS at 210 F., about 2.0 Weight percent of basic barium mahogany sulfonate, about 0.7 weight percent of Zinc dithiophosphate, about 0.6 weight percent of diamrylphenyl phosphate, and about 0.001 weight percent of a silicon polymer having a viscosity of 100 centistokes at 25 C.

References Cited in the file of this patent UNITED STATES PATENTS 1,850,700 Taylor Mar. 22, 1932 2,340,331 Knutson et al Feb. 1, 1944 2,364,283 Freuler Dec. 5, 1944 2,364,284 Freuler Dec. 5, 1944 2,369,632 Cook Feb. 13, 1945 2,418,422 Pamer Apr. 1, 1947 2,785,089 Lanteri Mar. 12, 1957 2,839,469 Pfeifer June 17, 1958 2,916,499 Vierk et a1 Dec. 8, 1959 

1. A METHOD FOR PROTECTING THE INTERNAL SURFACE OF A METAL TANK FROM THE CORROSIVE EFFECTS OF SALT LADEN AIR AND SALT WATER CRROSION CONSISTING ESSENTIALLY OF INTRODUCING INTO SAID TANK A FLUENT COATING COMPOSITION COMPRISING AN INTIMATE MIXTURE OF FROM 90.0 TO 98.5 WEIGHT PERCENT OF A MINERAL LUBRICATING OIL, FROM 0.5 TO 5.0 WEIGHT PERCENT BARIUM MAHOGANY SULFONATE, FROM 0.5 TO 1.8 WEIGHT PERCENT ZINC DITHIOPHOSPHATE AND FROM 0.3 TO 3.5 WEIGHT PERCENT ALKYL PHENYL PHOSPHATE, FLOATING SAID COATING COMPOSITION UPON THE SURFACE OF A BODY OF WATER IN SAID TANK AND COATING SAID INTERNAL SURFACES WITH SAID COATING COMPOSITION BY EFFECTING RELATIVE MOVEMENT BETWEEN THE SURFACE OF SAID BODY OF WATER AND SAID WALLS. 